this scene renderns remaind me a old 3d game, but now blender have very powerfull renderns , i suspect that you more study :
light
the lights not exist
modelling
(in skull image you have use a blender sculpt dyntopo? after you play with form, you rework to uniform the form)
shalder-texture nooot good
questions
-your pc config?
-your render engine?
my image with cycles render, the textures is not complicated, hand draw
10 passes of render 1minute on old mascine portable (dual core 2100mhz)
tre or four lights:
blue light (simulate the ambient light blue of sky)
red on down give a idea of yellow of sun reflected on floor
shadinng
if you use a prerendered images, why you don't use the tru power of render?
Bumpmap, normalmap, specular
modelling in this image not is present more vertex 14987, but the work is implantend more on texture, lights and shalder
is possible better, but i have realized this for an architect that say : "blender not goodd, bla bla bla , autodesk is better bla bla bla" i realized this in 20minutes with texture drawing ahahahha the architect have changed his mind
mission accomplished